The present invention relates to a pneumatic separator for flowable particulate materials, e.g., chaff from grain.
Pneumatic separators for this purpose are already known. For example, German Pat. DE No. 1,131,491 discloses a pneumatic separator in which a cylindrical housing surrounds a tubular separating channel the inner wall of which forms a container that is closed at the top and open at the bottom. Beneath this container and coaxially therewith, there is arranged a distributor body having a central passage and a conical guide face. An annular gap is provided between the body and the container for entry of the material into the separating channel. A central duct terminates beneath and at a distance from the body; the material to be processed is blown via compressed air through the central passage into the container and at the same time some of the air is branched off beneath the distributor body to enter laterally into the separating channel. A tube nipple concentrically surrounds the outlet end of the duct and conically diverges towards the distributor body; its inlet end communicates with the atmosphere and its outlet end, through which additional air is supplied into the separating channel, is shielded against the entry of material leaving the channel.
An analogous separator is disclosed in German Pat. DE No. 1,507,715. Here, the container arranged in the housing is of frustoconical shape, so that the separating channel converges in the flow direction of the separating air stream. An annular step is provided on the conical guide face of the distributor body to achieve a brief retardation of the particulate material, the aim being to assure that it enters into the separating channel in a constant flow and substantially uniformly distributed over the periphery of the body.
According to a proposal in German Gebrauchsmuster DE-GM No. 6,910,093 the material is supplied via a separate duct entering the container in the housing. Housing parts contacted by the material are provided with arrangements for cleaning them via airstreams, to prevent agglomeration of the material on these parts.
Finally, separators are known in which material is admitted from above via a central supply tube and the conical distributor body arranged under the outlet end of the tube can be moved relative to the tube counter to the action of an energy-storing device, so that it opens the outlet of the tube to a greater or lesser extent in dependence upon the weight of the column of incoming material acting upon it (U.S. Pat. No. 1,987,615 and British Pat. No. 715,176).
These prior-art devices are employed in a variety of applications, for example to separate chaff from grain, dust from grain and malt, substandard (shrivelled) kernels from acceptable ones, to clean and segregate granulates by fractions, and the like. In many of these applications the prior-art devices operate satisfactorily. However, when materials are involved which are difficult to separate pneumatically, such as e.g., dehusked cereals, it has been found in practice that they will produce only very limited results. Also, these devices are at least in some instances rather complicated and therefore also expensive. Dehusked crop mixtures of grains and legumes, e.g., oats, rice, soy beans, peas and the like, are difficult to separate because the kernels (grain, beans or peas) have very different floating speeds from the husks or shells or parts thereof.